spirula

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A small cephalopod mollusk of the genus Spirula, having a spirally coiled, partitioned internal shell.

Century Dictionary and Cyclopedia

1. n. In Cephalopoda: A genus of sepioid cuttlefishes, typical of the family Spirulidaæ, having a delicate shell in the hinder part of the body rolled into a flat or discoidal spiral, with discrete whorls whose involute spire presents ventrally, and no guard. There are several species, as S. lævis and S. fragilis. The shells are common, and are sometimes carried by the Gulf Stream to the coast of England, but specimens of the entire animal are extremely rare. Also Spirulæa, Spirulea.
2. n. A member of this genus.
3. n. In sponges, an irregular spineless polyact spicule of spiral form.

Wiktionary

1. n. zoology Any of the cephalopod genus Spirula

GNU Webster's 1913

1. n. (Zoöl.) A genus of cephalopods having a multilocular, internal, siphunculated shell in the form of flat spiral, the coils of which are not in contact.

WordNet 3.0

1. n. a small tropical cephalopod of the genus Spirula having prominent eyes and short arms and a many-chambered shell coiled in a flat spiral